PROJECT SUMMARY/ABSTRACT Dysregulation of RNA pathways is a common theme among many neurodegenerative diseases including SMA, ALS, CMT and SMARD1. The long-term objective of this project is to identify proteins that function within IGHMBP2 pathways and modify the SMARD1 (nmd) phenotype. The identification of these proteins will provide information on the native biological function of IGHMBP2, the role these proteins play in neuronal processes and neurodegeneration, and the potential development of therapeutic targets not only for SMARD1 but for other neurodegenerative diseases as well. This proposal uses two complementary approaches to examine the cellular pathways of IGHMBP2: 1) examine potential modifying genes contained within a BAC that rescues neurodegeneration in nmd mice, and 2) examine the functional significance of the Ighmbp2/Abt1 interaction. Approach 1: IGHMBP2 associates with several translation factors, including ABT1 and tRNAs. The significance of these interactions was further supported by the identification of a transgenic BAC clone that rescued the neurodegenerative phenotype in nmd (Ighmbp2 mutant) mice, but did not alter Ighmbp2 splicing or increase Ighmbp2 protein levels, revealing an important disease-associated function. Further delineation of this BAC demonstrated that an 18.1kb fragment contained the genes Abt1 and five tRNATyr genes. This proposal will specifically examine the ability of Abt1 and the tRNATyr to modify the nmd (SMARD1) phenotype in mice following AAV9 delivery of these genes. Approach 2: Biochemical studies have demonstrated IGHMBP2 associates with ribosomes and proteins involved in ribosome biogenesis, including ABT1, Reptin and Pontin. To functionally characterize the interaction between Ighmbp2 with Abt1, this proposal will systematically identify the ABT1-interacting domain within Ighmbp2, and subsequently identify mutations that abrogate this interaction. The Ighmbp2 mutations that fail to interact with Abt1 will then be reintroduced into the nmd mouse using AAV9 vectors to determine whether the Ighmbp2 /Abt1 complex is essential for rescue of the nmd phenotype.